Heretofore, the prior art using a permanent-magnet synchronous generator of this kind is disclosed in Patent Literature 1, for example. In this Patent Literature 1, there are provided an inverter module for controlling a three-phase AC motor being a permanent-magnet synchronous generator and current detection means for detecting electric current flowing through the inverter module. Further, a construction is taken that, when the current detection means detects electric current exceeding a current value determined in advance, the operation of the inverter module is discontinued and then, a short-circuited place at switching elements inside the inverter module is detected by the use of a switching pattern for short-circuit detection.